In automotive engineering, decentralized systems are often used for control, i.e., control systems including a plurality of control units which are locally distributed for controlling sub-components of the system to be controlled. Examples of this in automotive engineering include the control of brake systems, control of engines including multiple cylinder blocks, etc. In principle, all these decentralized control units process their control functions independently of one another. However, there are operating phases in which the activities of the decentralized control units are coordinated, e.g., when the overall system performs a pre-drive check or when special control functions are used to shut down the system as a whole.
German Published Patent Application No. 198 26 131 describes a decentralized control system on the example of a control system for operating the brake system of a motor vehicle. The structural features of this decentralized system include a pedal module for central detection of the driver's intent, four wheel modules for regulation of brake actuators for each wheel individually and a processing module for calculation of higher-level-brake functions (e.g., an electronic stability program). The individual modules communicate with one another through one or more communication systems. The internal structure of a wheel module includes various logic levels. A first logic level includes at least the calculation of the control and regulating functions for the wheel brakes, while the other logic levels contain various functions for computer monitoring and function testing of the first level. Calculation of the control and regulating functions may include different operating modes, depending on the regulating principle and the scope of function of the overall system. For example, if the wheel braking torque is used as a regulating variable, it is necessary to ensure that it is possible to control or regulate the wheel brake even when the vehicle is at a standstill, although no wheel braking torque is it detectable when the vehicle is at a standstill.
German Published Patent Application No. 199 37 156 also relates to the control of a brake system, but it describes a different structure of such a decentralized control system. According to that patent, a wheel brake module which implements the control and regulating functions is assigned to each of the four wheel brakes. There is no central detection of the driver's intent here. Instead, at least one actuation signal of the brake pedal is sent to each wheel brake module. The wheel brake modules communicate via at least one communication system.
German Published Patent Application No. 198 26 134 describes the control of a wheel brake as part of a wheel braking torque regulating circuit which switches from wheel braking torque regulation to angle-of-rotation regulation or position regulation on detecting that the vehicle is at a standstill. When the vehicle velocity drops below a vehicle limiting velocity from which it is deduced that the vehicle is at standstill or that standstill is immediately imminent, a fictitious actual braking torque is determined from the measured angle of rotation of the motor of the wheel brake actuator and/or the position of a movable element in the area of the wheel brake or the actuator, and this fictitious actual braking torque is sent to the braking torque regulator as an actual input variable.